The **apt* command makes a cache in your HDD consisting of all downloaded data.
So it gets bigger and bigger after certain of time.
This makes the system slow and sluggish.
To remove all those caches from your system HDD, run the following command.
sudo apt-get clean
Don’t get worried. It does not delete any installed application from your system.
Application “dependencies” is another concern. When an application is installed, other related small application also installed along with to have to full functionality. But if you uninstall the application that time the dependencies or small subsidiary application will not be removed.
So it creates junk files on the HDD and slows the system. To clean up all these unnecessary packages or unwanted “Dependencies” from the system, run the command.
sudo apt-get autoremove